This invention relates generally to an electrochromic display device, and more particularly to an electrochromic display device in which the electrochromic layer is deposited by a technique known as oblique evaporation.
Electrochromic devices are well-known devices which exhibit a phenomenon known as "persistent electrochromism", e.g. see U.S. Pat. No. 3,521,941 entitled, "Electro-Optical Device Having Variable Optical Density", issued July 28, 1970. The term "persistent electrochromism" denotes the property of a material whereby its electromagnetic radiation absorption characteristic is altered, in most instances, even at ambient temperature, under the influence of an electric field.
Such materials, for example, may exhibit little or no absorption of visible wavelength in the absence of an electric field and therefore be transparent, but when subjected to an electric field, effectively absorb in the red end of the electromagnetic spectrum, turning blue in color. Similar effects can be observed in other portions of the electromagnetic spectrum, invisible as well as visible.
There have been numerous studies of the electrochromic process which occurs at the electrochromic electrode. Various attempts to utilize the electrochromic devices, such as in numerical displays, have been made, but most attempts have been discouraged by defects of the electrochromic devices, e.g. slow coloring and bleaching response, and short cycle lifetime of coloring and bleaching.